In this case though I'm talking of a COBOL backend very old windows app.

We want to move data from COBOL files to a database, we're making our own migration tools/scripts in python (In order to mainly rename weird name table/column names to sanish ones), and we can target any SQL flavour/database we want to insert that data at.. the question is what's the better call here...

SQLite seems pretty good enough, at least until we can move our whole app to a more web-friendly environment at which point something like postgres might make more sense? but that could take a couple years... (we're a small team/company in a very specific niche/locale)